Many ophthalmic surgical laser systems use a patient interface to immobilize the eye the surgery is performed on. A patient interface typically includes a contact lens, directly disposable on the cornea to guide the laser beam into the eye. The contact lens can be affixed to the eye with a vacuum suction ring or skirt that suppresses the motion of the eye relative to the contact lens. Once the contact lens is in place, the laser system scans a surgical laser beam along a selected or predetermined surgical pattern to create cuts in the ophthalmic target tissue.
Some systems employ a one-piece patient interface (“PI”) which is rigidly fixed to an objective of the laser system. In others, a two-piece or multi-piece PI is employed, where a top portion of the PI is fixed to the laser system, while a bottom portion is affixed to the eye in preparation for the surgical procedures. Subsequently, the top and bottom portions can be coupled to conveniently align the eye with the objective. Finally, there are laser systems where the structure allows some degree of transverse or lateral movement of the PI relative to the laser system to assist the alignment of the eye.
The surgical patterns are sometimes referenced to the contact lens, sometimes to the objective of the laser system, and in yet other systems, to an internal reference of the laser system. For example, the center of the surgical pattern maybe aligned with the center of the contact lens. Therefore, the precise placement and targeting of the surgical pattern into the eye is critically dependent on the precise docking of the contact lens. As part of the docking, in one piece PIs the contact lens is to be aligned with the optical axis of the eye and with the center of the cornea. In two piece PIs, in addition, once the contact lens is docked in an aligned position to the eye, the top and bottom portion of the PI need to be aligned as well. Finally, in transversely movable PIs, the PI is to assume an essentially central position at the end of docking.
Some laser systems used for corneal procedures, such as LASIK procedures, employ essentially flat or planar, contact lenses. These lenses flatten the cornea when affixed to it with pressure and vacuum suction. Therefore, if the contact lens is docked with a transverse or lateral misplacement to the cornea, the surgical pattern will be placed into the eye with a lateral shift from the center. However, since the cornea itself is flattened, this lateral shift reduces the precision only to a limited degree.
In contrast, in advanced ophthalmic surgical systems the misaligned docking of the contact lens can cause more serious challenges in several aspects.